docs: def process_request(self, request):
          """
          Sets the current request's ``urlconf`` attribute to the urlconf
          associated with the subdomain, if it is listed in
          ``settings.SUBDOMAIN_URLCONFS``.
          """
          super(SubdomainURLRoutingMiddleware, self).process_request(request)
  
          subdomain = getattr(request, 'subdomain', UNSET)
  
          if subdomain is not UNSET:
              urlconf = settings.SUBDOMAIN_URLCONFS.get(subdomain)
              if urlconf is not None:
                  logger.debug("Using urlconf %s for subdomain: %s",
                      repr(urlconf), repr(subdomain))
                  request.urlconf = urlconf